I am familiar with lath and plaster but have no idea what this stuff is called to even begin to research how to repair it.

It is on the inside of double walled brick construction of my 1915 bungalow. It is about 1-1 1/4 inches thick and is a white plaster type material that is mixed with tiny pebbles and applied directly to the brick. It is extremely soft and has no lath. Maybe lime based? I tried spraying it with water and compressing it to see if it would reharden but it did not (like I would expect lime to do.)

I am looking to find out what it is to determine how I should repair it. I could remove it but I am concerned that removing it would effect the integrity of the hundred year old lime based mortar holding the bricks together.

Any thoughts?